The present invention relates to a novel absorbent article such as a sanitary napkin having an absorbent structure which is characterized by having an integral high absorbency zone.
Absorbent structures are known for inclusion in disposable absorbent articles used for absorbing body fluids and other exudates. Such absorbent structures have traditionally been made from readily available and relatively inexpensive materials such as cotton fibers, wood pulp fluff, cellulosic tissue or wadding, or other absorbent fibers. These materials have provided satisfactory absorbency of fluids both in terms of absorbency rate and overall absorbent capacity. Unfortunately, absorbent structures made from such materials may tend to collapse when wetted, thereby losing some of their void volume. Such structures may also allow absorbed fluid to be squeezed back out of the structure onto the user of the absorbent article. Furthermore, when such structures have absorbed fluid, they may present an uncomfortable wet feeling against the skin of the user.
More recently, superabsorbent polymer particles have been combined with the more traditional absorbent materials to provide structures with enhanced absorbency and retention, which may help to eliminate the problems of squeeze-out and wet surface feel. Replacement of traditional absorbent materials with superabsorbent polymer particles may also allow for absorbent products to be thinner while retaining the absorbent capacity of thicker, bulkier products. A drawback to superabsorbent polymer particles, however, is their relatively high cost compared to the more traditional absorbent materials.
Additionally, since superabsorbent polymer particles tend to swell as they absorb fluid, they may cause what is commonly known as gel-blocking. In other words, as fluid is absorbed by the particles of superabsorbent polymer, those particles swell and may form an occlusive layer of swollen superabsorbent particles. This occlusive layer then prevents the passage of additional fluid into the structure. Thus, the superabsorbent polymer particles must be properly placed within an absorbent structure to allow for this swelling and to most fully utilize their absorbent capacity. Generally, prevention of gel-blocking has been realized by mixing superabsorbent polymer particles with spacer materials, such as absorbent or nonabsorbent fibers, or by placing the superabsorbent polymer particles toward the bottom of the absorbent structure. However, although these methods of superabsorbent polymer placement may minimize gel-blocking, they do not effect the most efficient use of the superabsorbent polymer""s absorbent capacity.
Therefore, what is needed is an absorbent structure with good absorbency and retention of fluid. What is also needed is an absorbent structure which will help to provide a dry feel to the skin of a user when used in an absorbent article. What is further needed is an absorbent structure with superabsorbent polymer particles spaced and placed within the structure to most fully utilize the absorbency and retention capabilities of the superabsorbent polymer particles.
It is an object of the present invention to provide an absorbent article with good absorbency and retention of fluid which will help to provide a dry feel to the skin of a user of the article.
It is another object of the present invention to provide an absorbent structure with superabsorbent polymer particles spaced and placed within the structure to most fully utilize the absorbency and retention capabilities of the superabsorbent polymer particles.
In accordance with the present invention, there has been provided a novel absorbent structure for use in absorbent articles. The absorbent structure includes an absorbent element formed from absorbent fibers and may optionally include additional laminate layers such as one or more layers of a nonwoven fabric. The nonwoven fabric may have a lower density and a higher porosity than the absorbent element of the invention to allow for fluid acquisition and the transfer of the acquired fluid to an adjacent, higher density absorbent element. Alternatively, the nonwoven fabric may have a higher density and a lower porosity than the absorbent element to increase fluid wicking throughout the nonwoven fabric. Preferably, lower-density nonwoven fabrics are placed adjacent the body-facing surface of an absorbent element, and higher-density nonwoven fabrics are placed adjacent the garment-facing surface of an absorbent element.
The absorbent structure has peripheral edges and a center region. The center region is that portion of the structure which is inward from the edges of the structure and which is intended accept incoming fluid when the structure is used in an absorbent articles. The peripheral edges are those portions of the structure which are adjacent its periphery.
The absorbent element has an upper surface and a lower surface defining therebetween an element thickness. The absorbent element thickness has an upper 35% and a lower 65%. The absorbent element further has an integral structure having a zone of high absorbency which comprises an integral mixture of absorbent fibers and superabsorbent polymer particles and has a first surface and a second surface separated by a zone thickness. As used herein, the terminology xe2x80x9cintegralxe2x80x9d means a unitary structure wherein the absorbent fibers are intermeshed throughout the entire absorbent element. Thus, there are no identifiable laminate layers which are separable from other layers within the element.
The high absorbency zone is located in at least a portion of the center region of the absorbent element and within the upper 35% of the absorbent element. The first surface of the high absorbency zone may optionally be coplanar with the upper surface of the absorbent element, or alternatively, the high absorbency zone may be below the upper surface of the absorbent element, provided of course that the high absorbency zone is within the upper 35% of the thickness of the absorbent element. The thickness of the high absorbency zone may comprise up to about 35% of the thickness of the absorbent element, the remaining 65% of the absorbent element being substantially free of superabsorbent particles. Thus, the absorbent element comprises an upper high absorbency zone containing absorbent fibers and superabsorbent polymer particles located in an upper 35% of the thickness of the absorbent element and a lower absorbent region which is substantially free of super absorbent particles.
In a preferred embodiment, the superabsorbent polymer particles may be mixed with absorbent fibers within the high absorbency zone. In a most preferred embodiment, the superabsorbent polymer particles are uniformly and homogeneously mixed with the absorbent fibers within the high absorbency zone. Alternatively, the superabsorbent particles may be located within the high absorbency zone in a relatively narrow region comprising 15%, or more preferably 10%, of the absorbent element thickness. Additionally, the superabsorbent particles may be distributed within the high absorbency zone on an increasing gradient wherein the concentration of superabsorbent particles increases from the first surface of the high absorbency zone to the second surface of the high absorbency zone, or a decreasing gradient, wherein the concentration of superabsorbent particles decreases from the first surface of the high absorbency zone to the second surface of the high absorbency zone. In a most preferred embodiment the upper surface of the absorbent element is substantially free of superabsorbent particles, the high absorbency zone being slightly below the upper surface of the absorbent element wherein the upper surface including up to about 15% of the thickness of the absorbent element comprises 100% absorbent pulp fibers.
The absorbent structure is useful in absorbent articles such as sanitary napkins, diapers, incontinence articles and the like. An example of such an article comprises the absorbent element of the invention contained between a liquid-permeable body-facing layer and a liquid-impermeable barrier layer and positioned such that the body-facing layer is adjacent the upper surface of the absorbent element and the impermeable barrier layer is adjacent the lower surface of the absorbent element.